Naturally occurring clays such as smectites, vermiculites and bentonites are composed of semicrystalline aluminosilicate layers (lamellae) held together by Van der Waals and electrostatic forces. Anionic charges on the siliceous layers are neutralized by cations in the interlamellar spaces. These cations, usually Na.sup.+, Ca.sup.+2, can be ion exchanged with large inorganic cations such as Fe.sup.+3, Cr.sup.+3 or with metal hydroxy polymer cations such as [Al.sub.13 O.sub.4 (OH).sub.24 (H.sub.2 O).sub.12 ].sup.+7 or [Zr(OH).sub.2.4H.sub.2 O].sub.4.sup.8+. The polymeric cations act as pillars, propping the clay layers apart.
Pillared clays are known to catalyze numerous reactions such as alkylation, cracking, ester formation, dimerization, oligomerization, etc. A review of the reactions catalyzed by pillared clays may be found in an article by J. M. Adams, Applied Clay Science, 2, pp. 309-342 (1987). Of these reactions, alkylation has received considerable attention. For example, U.S. Pat. No. 4,499,319 discloses layered clays such as montmorillonite which have been ion-exchanged with metal cations such as chromium and aluminum, which are used to alkylate aromatic compounds. Other examples include U.S. Pat. No. 4,605,806 which discloses a hydrogen ion-exchanged pillared clay; U.S. Pat. No. 3,965,043 discloses a metallic cation exchanged trioctahedral 2:1 layer-lattice smectite-type clay and U.S. Pat. No. 3,979,331 which discloses a metallic cation exchanged synthetic hectorite-type clay useful for alkylating aromatic hydrocarbons.
Another reference is U.S. Pat. No. 4,499,195 which discloses a co-gel of a smectite clay with an inorganic metal oxide to produce a co-gel. The inorganic oxides include Group IV-B metal oxides and other oxides such as silicon, aluminum, thorium and uranium. However, since the metal oxide gel is stated to be formed before addition of the clay, it appears that the clay is not homogeneously dispersed in the metal oxide gel. A continuation-in-part of the '195 reference (U.S. Pat. No. 4,587,009) discloses the use of the co-gel for hydrogenation of hydrocarbons.
U.S. Pat. No. 4,111,846 discloses a catalyst that contains a zeolite as the active material and a clay as a "weighting" agent. Apparently what is meant by a "weighting" agent is a filler which is used to increase the density of the catalyst. Finally, U.S. Pat. No. 4,844,790 discloses a delaminated clay. The patentee, in passing, states that the catalyst may include a zeolite and/or a refractory oxide component as part of the catalyst. The catalyst is prepared by spray drying.
In contrast to this prior art, applicants have prepared a composition which contains a clay (pillared or non-pillared) homogeneously dispersed in an inorganic oxide matrix. The inorganic oxides which may be used as the matrix material include alumina, titania, silica, zirconia, P.sub.2 O.sub.5 and mixtures thereof. A preferred method of preparing the composition involves dispersing the clay in a sol of the element which is the precursor of the oxide, thereby providing a mixture which can be formed into particles such as spheres by methods such as oil dropping, followed by calcination to form a metal oxide matrix with a clay dispersed therein. The composition has increased activity versus an untreated clay.
As will be discussed more fully herein, the inorganic oxide matrix completely surrounds the clay layers such that they are delaminated and truly homogeneously dispersed, on a one micron scale, throughout the inorganic oxide matrix. It is the use of a hydrosol which gives rise to this homogeneity which cannot be obtained by extruding or spray drying physical mixtures of a clay and a metal oxide. In fact, applicants have found that a composition of the present invention containing an acid washed montmorillonite clay in an alumina matrix has better activity than a physical mixture of the clay and alumina.